Superchargers are air pumps or blowers in the intake system of an internal combustion engine for increasing the mass flow rate of air charge and consequent power output from the engine. A turbosupercharger (normally called a turbocharger) is a supercharger with a turbine driven by engine exhaust gas. When superchargers are driven mechanically from the shaft of the internal combustion engine, a speed increasing gear box or belt drive is needed. Such superchargers are limited to a relatively low rotating speed and are large in size. Paxon Blowers and Vortech Engineering Co. are marketing such superchargers. Fixed gear ratio superchargers suffer from two very undesirable features: 1) there is a sharp decrease in boost pressure at low engine RPM because boost pressure goes generally to the square of the speed of rotation, and 2) it is generally difficult to disconnect the supercharger from the engine when the supercharger is not needed.
Most automobiles are not supercharged, i.e., air is sucked into the engines merely by vacuum created by action of the engine's pistons. Some selected models are turbocharged or supercharged for improved engine performance. Most diesel engine driven trucks and buses are turbocharged. At low engine speed many of these engines suffer from a lack of air flow especially during periods of acceleration. During these periods particulate emission can be a severe problem and attempt to avoid the emissions tend to result in poor acceleration.
The Applicant has been issued U.S. Pat. No. 5,471,965 for a very high speed radial inflow hydraulic turbine useful for motor vehicle supercharging and U.S. Pat. No. 5,421,310 for a hydraulic supercharging system. Both of these patents are hereby incorporated by reference herein. In typical situations, hydraulic superchargers are most effectively used on motor vehicles in conjunction with turbochargers. Over certain ranges the turbocharger can handle efficiently the job of supplying air to the engine and over certain ranges it needs the help of the supercharger. Maximum effectiveness is provided when a good simple control system is provided which takes advantages of the best attributes of both the supercharger and the turbocharger. It is in some cases desirable to be able to change the supercharging pressure into the engine in a manner independent of engine speed.
What is needed, is a good simple system for controlling supercharger performance on typical motor vehicles.